The present invention relates generally to a composition which is activated by electromagnetic energy to provide controlled sustained generation and release of at least one gas. The invention particularly relates to a composition including an energy-activated catalyst and anions capable of being oxidized by the activated catalyst surface or subsequent reaction product to generate a gas, for retarding, controlling, killing or preventing microbiological contamination (e.g., bacteria, fungi, viruses, mold spores, algae, and protozoa), deodorizing, enhancing freshness, and/or retarding, preventing, inhibiting, or controlling chemotaxis by release of a gas or a combination of gases, such as chlorine dioxide, sulfur dioxide, nitrogen dioxide, nitric oxide, nitrous oxide, carbon dioxide, hydrogen sulfide, hydrocyanic acid, dichlorine monoxide, chlorine, or ozone.
Photocatalysts are generally used to catalyze oxidation and reduction reactions, such as the degradation of organic compounds which contaminate air or water. When exposed to ultraviolet radiation in the presence of a semiconductor, water, oxygen and hydroxide anions can be converted to peroxide anions and hydroxyl radicals. These species can further react with an organic compound that ultimately forms carbon dioxide and water. Carbon dioxide is generated by the decomposition of organic matter, not by the oxidation of anions.
A photocatalyst increases the production of hydroxyl radicals to catalyze decomposition of the organic compounds. When a photon is absorbed by a semiconductor photocatalyst, an electron is promoted from the valence band to the conduction band, producing a valence band hole. The hole and the electron diffuse to the surface of the photocatalyst particle where each may chemically react. Valence band holes either oxidize organic compounds or oxidize adsorbed water molecules to generate hydroxyl radicals. Examples of such use of photocatalysts include Nachtman et al., U.S. Pat. No. 5,868,924 (reduction of total organic carbon content by passing water through a water purifier chamber containing a photocatalyst); Matthews, U.S. Pat. No. 5,244,811, and Zhang et al., U.S. Pat. No. 5,501,801 (methods for photocatalytic oxidation of organic contaminants in a fluid by contacting the fluid with a photocatalyst-coated surface to decompose the contaminants); Tanaka et al., U.S. Pat. No. 5,658,841 (conversion of organics to carbon dioxide by exposing a liquid to a photocatalyst); Heller et al., U.S. Pat. Nos. 5,616,532, 5,849,200 and 5,854,169 (compositions containing photocatalysts and substantially non-oxidizable binders that are used to remove organic contaminants from air, water or a surface coated with the composition); Watanabe et al., U.S. Pat. No. 5,874,701 (photodecomposition of bacteria or airborne substances that contact a wall or floor coated with a photoactive film); and Mouri et al, U.S. Pat. No. 5,872,072, and Linkous, U.S. Pat. No. 5,880,067 (photocatalysts for deodorizing or decontaminating a surface by decomposing malodors such as ammonia or hydrogen sulfide, or microbial contaminants, such as algae, fungi or bacteria, in air or a liquid that contacts the surface).
Photocatalysts have also been used in electrochemical photocells to generate gases in electrolyte solutions using an electrical current. Inoue et al., “Competitive Photosensitized Oxidation at TiO2 Photoanode,” Chemistry Letters, 1073-1076 (1977) describe photoelectrochemical oxidation of halide ions, such as chloride anions, in an electrolyte solution.
Chlorine dioxide and other biocidal gases have also been generated and released through the use of an activator that provides hydronium ions which then react with a precursor to form the gas. Ripley et al., U.S. Pat. No. 5,736,165 describe two component systems including a liquid component containing a chlorine dioxide precursor, such as a metal chlorite, and an activator component, such as a transition metal or acid. The components are separated until use to prevent premature formation of chlorine dioxide. When the components are combined, the hydronium ions react with the chlorine dioxide precursor to form chlorine dioxide.
Compositions that are moisture activated to generate and release chlorine dioxide gas or other gases are described by Wellinghoff et al. in U.S. Pat. Nos. 5,360,609, 5,631,300, 5,639,295, 5,650,446, 5,668,185, 5,695,814, 5,705,092, 5,707,739, and 5,888,528, and copending U.S. patent application Ser. Nos. 08/651,876, 08/724,907, 08/858,860, 08/921,357, 08/924,684, and 09/138,219. These compositions contain anions that react with hydronium ions to generate and release a gas. Such compositions need to be protected from moisture during production, storage and shipment to prevent premature gas generation and release.
There is a need for an inert composition that can be easily activated to initiate generation and release of chlorine dioxide or another gas in use. A composition that, except for the anions therein for generating the gas, is composed of and reacts to provide residues composed of only substances usable in foods, or those generally recognized as safe or inert substances, is particularly needed for food packaging, modified atmosphere packaging, and other applications where the substances can be ingested by or in contact with humans. Although the Wellinghoff et al. moisture-activated compositions are effective biocides and deodorants, there is a need for compositions that are more readily manufactured, easily activated and deactivated to provide more control or flexibility for controlled sustained generation and release of a gas, and easily transported and stored prior to use without the need for avoiding exposure to atmospheric moisture. There is also a need for a composition that can generation and release a gas when completely encapsulated in a hydrophobic material.